Needle bearing cage and method for producing the same

ABSTRACT

The invention relates to a window cage ( 1 ) for a needle bearing. The pockets ( 5 ) of said window cage are formed by punched out sections and by a stamping process with material displacement in a cage strip ( 9 ) which is then bent round. According to the invention, the window cage ( 1 ) is characterized in that before the cage strip ( 9 ) is bent, the opposite surfaces of the web walls of a pocket ( 5 ) are made up of three sub-surfaces ( 10, 11, 12 ) in the area of the retaining projections ( 7, 8 ). The first two sub-surfaces ( 10 ) follow a course which is parallel to a middle vertical ( 13 ) and each extend into a second sub-surface ( 11 ) at their upper end, said second sub-surface running diagonally in the direction of the central point of the pocket. Each of the second sub-surfaces then ends in a third sub-surface ( 12 ) which also runs parallel to the middle vertical ( 13 ).

This application is a 371 of PCT/EP98/06783 filed Oct. 26, 1998.

FIELD OF THE INVENTION

The invention concerns a cylindrical window-type cage for a needleroller bearing.

BACKGROUND OF THE INVENTION

A generic cage of the pre-cited type is known from DE-GM 18 29 610. Thiscylindrical window-type cage is made of a strip into which at firstpockets are punched which are then deformed with a stamping tool so thatwhen the metal strip is bent to form a cage, retaining projections areformed which prevent the needle rollers from falling out of the cage inoutward direction. The retention of the needle rollers in inwarddirection is effected by the inclined walls of the crossbars. Thematerial displacement which is initiated by the additional stampingprocess is such that material is displaced from the inside towards theoutside so that after completion of the stamping process, the cagepocket, as seen in cross-section, ends in a roof-shape i.e., it taperstowards the outside.

A disadvantage of this is that, especially in bearing cages with a smalldiameter, the strong bending of the strip can lead to a clamping of therolling elements in the pocket. A further disadvantage is that thisshape of the pockets makes it more difficult to fill them with therolling elements.

SUMMARY OF THE INVENTION

The object of the invention is therefore to provide a pocket shapewhich, particularly in the case of cages with a small diameter, permitsa simple manufacturing of the bearing.

The invention achieves this object by the fact that in the unbent stateof the cage strip, the surfaces of the crossbar walls of a pocketsituated opposite each other are formed in the region of the retainingprojections with three partial surfaces such that the first partialsurfaces are parallel to a central vertical line and merge at theirupper ends into inclined second partial surfaces pointing towards thecenter of the pocket, each of the second partial surfaces ending in athird partial surface which is likewise parallel to the central verticalline.

In this type of pocket configuration in which the retention of therolling elements in inward direction is effected by the inclination ofthe crossbar walls and in outward direction by the retainingprojections, the needle roller bearing cage is reliably guided on thepartial surfaces situated in the middle and inclined towards each other.The configuration of the cross-section of the pockets according to theinvention has the further advantage that, in small bearing cages whichnecessitate a very strong bending of the cage strip, no cracks andundesired deformations occur in the region of the pockets. A furtheradditional advantage is that, due to the enlarged clear width of thepocket in upward direction, a more favorable elastic snapping-in of theneedle rollers into the cage is possible.

The ratio of the diameter D_(L) of the needle rollers to the pitchcircle diameter D_(TK) is≧1:6. This means that the stamped pockets canbe used particularly advantageously in cages having a small diameteri.e., in cages in which the original strip is subjected to a strongbending.

The manufacturing of a needle roller bearing cage is effected by thefollowing steps:

punching a cage strip to form pockets defined by crossbars for thereception of the needle rollers,

introducing a tong-like stamping tool with two stamping jaws intoadjoining pockets, pressure-loading said tool so that a displacement ofmaterial takes place such that, in the region of the retainingprojections, opposing surfaces of the crossbar walls of a pocket areformed with three partial surfaces such that the two first partialsurfaces are parallel to a central vertical line and merge at theirupper ends into inclined second partial surfaces pointing towards thecenter of the pocket, each of the second partial surfaces ending in athird partial surface which is likewise parallel to the central verticalline,

cutting off a length of the cage strip to obtain a ratio of the diameterD_(L) of the needle rollers to the pitch circle diameter D_(TK) of>1:6,

bending round the cage strip in a direction opposite to that of thematerial displacement and, if necessary, joining the abutting ends ofthe cage to each other.

Further, in the unbent state of the cage strip, the surfaces of thecrossbar walls of a pocket situated opposite each other are formed inthe region of the retaining projections with three partial surfaces suchthat the first partial surfaces are inclined relative to a centralvertical line and point towards the center of the pocket while mergingat their upper ends into second partial surfaces that are parallel tothe central vertical line, each of the second partial surfaces ending ina third partial surface which is likewise inclined.

Due to this configuration of the pocket in the cage strip, the bentround cage can be filled with needle rollers without any problem fromthe inside, while the previously described cage shapes are mainlyintended for the filling of the needle rollers from the outside. Themanufacture of such a cage is effected in a manner analogous to thealready described methods.

Finally, in the unbent state of the cage strip, the surfaces of thecrossbar walls of a pocket situated opposite each other are formed inthe region of the retaining projections with three partial surfaces suchthat the first partial surfaces are inclined relative to a centralvertical line towards the center of the pocket and merge at their upperends into likewise inclined second partial surfaces, each of the secondpartial surfaces ending in a third partial surface which is parallel tothe central vertical line.

To conclude, the crossbars are profiled. As known, this means that thecrossbars connecting the two side rings do not extend in one continuoushorizontal line but are offset in upward or downward direction in a partof their axial length so that a horizontal portion is formed outside orinside the pitch circle, said horizontal portion being limited by twoportions of the crossbar which extend at an angle to the bearing axis.

The invention will now be described more closely with reference to thefollowing examples of embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a needle roller cage according to the inventionshown partly in section,

FIGS. 2, 4, and 7 show sections taken along line A—A of FIG. 1 and FIG.6 respectively, in the unbent state of the cage strip,

FIGS. 3, 5, and 8 show sections taken along line A—A of FIG. 1 and FIG.6 respectively, in the bent state of the cage strip, and

FIG. 6 is a side view of an offset cage shown partly in section.

DETAILED DESCRIPTION OF THE DRAWINGS

The window-type cage identified at 1 in FIG. 1 comprises two side rings2 and 3 which are connected to each other by a plurality of crossbars 4spaced uniformly over the periphery. The pockets 5 thus formed forreceiving the needle rollers 6 are defined by the side rings 2 and 3 andthe crossbars 4. Along their axial length, the crossbars 4 comprise tworetaining projections 7 and 8 which are spaced apart from each other andretain the needle rollers 6 in the pocket 5 in outward direction.

As can be seen from FIG. 2, in the unbent state of the cage strip 9, thesurfaces of the crossbar walls, or of the pockets 5, situated oppositeeach other comprise the three partial surfaces 10, 11, 12 in the regionof the retaining projections 7, 8. At its lower end, the pocket 5 isdefined by first partial surfaces 10 which are parallel to a centralvertical line 13 and merge at their upper ends into second partialsurfaces 11 which are inclined towards each other and which, in turn,merge into opposite third partial surfaces 12 which are likewiseparallel to the central vertical line 13. In this way, as seen insection, a funnel-shaped pocket 5 is formed which tapers in upwarddirection and thus has the widest opening at its lower end.

If now, as can be seen from FIG. 3, the cage strip 9 is bent downwardsto form a cylindrical window-type cage 1, the shape of the pocket 5 alsochanges. Due to the bending, the first partial surfaces 10 are no longerparallel to each other but bent inwards towards the center of thebearing. It is assured, in this way, that the needle rollers 6 cannotexit from the pocket 5 in radially inward direction i.e., the retentionof the needle rollers 6 is effected by the inclination of the firstpartial surfaces 10, the clear space between which is slightly smallerthan the diameter of the needle roller 6. Due to the bending, theinclination of the second partial surfaces 11 also changes i.e., theirdeviation from the central vertical line 13 is smaller than in FIG. 2.During the operation of the bearing, the needle rollers 6 are mainlyguided on these second partial surfaces 11 in the region of the pitchcircle. Finally, the third partial surfaces 12 also change theirposition due to the bending of the cage strip 9 such that the clearwidth of the pocket 5 at the outer periphery of the cage strip 9 or thewindow-type cage 1 is enlarged after bending. This enlargement permitsan unproblematic insertion of the needle rollers 6 into the window-typecage 1 from the outside. The clear space between the third partialsurfaces 12 in their region adjoining the partial surface 11, however,is only slightly smaller than the diameter of the needle rollers 6 sothat these can be snapped into the pocket 5 in the elastic region thusavoiding damage to the retaining projections 7, 8 or to therolling-contact surfaces of the needle rollers 6.

Such a window-type cage 1 is made by at first punching out pockets 5 outof a flat cage strip 9 with a punching tool. The pocket edges thusobtained are parallel to the central vertical line 13 i.e., they extendalong the vertical line 14 represented as a broken line in FIG. 2.Stamping is carried out in a known manner by introducing one or morestamping tools into adjacent pockets 5 and applying a force to the toolsso that the crossbar 4 separating the two pockets 5 is plasticallydeformed on both sides. Pressure is applied to the crossbar 4 along itsaxial length from both sides by a stamping tool whose contourcorresponds to the desired contour of the retaining projections 7, 8 tobe formed, and thus also to the contour of the partial surfaces 10, 11,12. These stamping tools are then moved towards each other so that aplastic displacement of material takes place in upward direction, thatis to say, as can be seen from FIG. 2, from the region 15 into theregion 16. After the pockets 5 have been stamped, the cage strip 9 iscut to the required length, bent into a round shape and, if necessary,its two abutting ends are joined firmly to each other.

FIGS. 4 and 5 illustrate the pocket shape described in a secondembodiment. In this case, in the unbent state of the cage strip 9, thepocket 5 again begins at its lower end with the first partial surfaces12 which, however, are inclined towards the center of the pocket 5 andmerge at their upper ends into the second partial surfaces 10 which areparallel to the central vertical line 13. These, in turn, merge at theirupper ends into the third partial surfaces 11 which are inclined towardsthe central vertical line 13. In this way, a funnel-shaped pocket 5 isobtained which, however, differs from the pocket illustrated in FIG. 2in the aforesaid manner. By this configuration of the first partialsurface 12 it is assured that the needle rollers 6 can be snappedelastically into the pockets 5 radially from the inside. The falling-outof the needle rollers 6 in inward direction is prevented in this case bythe partial surfaces 10, the clear space between whose lower ends isonly slightly smaller than the diameter of the needle roller 6. Thislikewise assures that the needle rollers 6 can be inserted into thepockets 5 of the window-type cage 1 in the elastic region from theinside.

FIGS. 6, 7 and 8 show the cage 1 described in a third embodiment. Thecentral portion of the crossbars 4 of this cage is offset towards thecenter of the bearing so that a falling-out of the needle rollers 6 inoutward direction is prevented by the retaining projections 7 and 8, andin inward direction, by the inclination of crossbars 4 i.e., by theiroffset portions. In the unbent state of the cage strip 9, the pocket 5is configured such that the first partial surface 10 a is inclined at adefined angle to the central vertical line 13 and merges at its upperend into the second partial surface 11 which is inclined furtherrelative to the first partial surface 10 a towards the central verticalline 13. The second partial surface 11, in turn, merges at its upper endinto a third partial surface 12 which is parallel to the centralvertical line 13.

What is claimed is:
 1. A cylindrical window-type cage (1) for a needleroller bearing which receives the needle rollers (6) in pockets (5)uniformly spaced from one another by crossbars (4), said pockets (5)being formed by punching and by stamping with displacement of materialin a cage strip (9) so that after the bending round of the cage strip(9) the needle rollers (6) are retained in inward direction by theinclination of the crossbar walls and in outward direction by retainingprojections (7, 8), characterized in that, in the unbent state of thecage strip (9), the surfaces of the crossbar walls of a pocket (5)situated opposite each other are formed in the region of the retainingprojections (7, 8) with three partial surfaces (10, 11, 12) such thatthe first partial surfaces (10) are parallel to a central vertical line(13) and merge at their upper ends into inclined second partial surfaces(11) pointing towards the center of the pocket, each of the secondpartial surfaces (11) ending in a third partial surface (12) which islikewise parallel to the central vertical line (13).
 2. A cylindricalwindow-type cage (1) according to claim 1, characterized in that theratio of the diameter D_(L) of the needle rollers (6) to the pitchcircle diameter D_(TK) is >1:6.
 3. A cylindrical window-type cage (1)for a needle bearing which receives the needle rollers (6) in pockets(5) uniformly spaced from one another by crossbars (4), said pockets (5)being formed by punching and by stamping with displacement of materialin a cage strip (9) so that after the bending round of the cage strip(9), the needle rollers (6) are retained in inward direction by theinclination of the crossbar walls and in outward direction by retainingprojections (7, 8), in the unbent state of the cage strip (9), thesurfaces of the crossbar walls of a pocket situated opposite each otherare formed in the region of the retaining projections (7, 8) with threepartial surfaces (10, 11, 12) such that the first partial surfaces (12)are inclined relative to a central vertical line (13) and point towardsthe center of the pocket while merging at their upper ends into secondpartial surfaces (10) that are parallel to the central vertical line(13), each of the second partial surfaces (10) ending in a third partialsurface (11) which is likewise inclined.
 4. A cylindrical window-typecage (1) for a needle bearing which receives the needle rollers (6) inpockets (5) uniformly spaced from one another by crossbars (4), saidpockets (5) being formed by punching and by stamping with displacementof material in a cage strip (9) so that after the bending round of thecage strip (9) the needle rollers (6) are retained in inward directionby the inclination of the crossbar walls and in outward direction byretaining projections (7, 8), in the unbent state of the cage strip (9),the surfaces of the crossbar walls of a pocket (5) situated oppositeeach other are formed in the region of the retaining projections (7, 8)with three partial surfaces (10, 11, 12) such that the first partialsurfaces (10) are inclined relative to a central vertical line (13)towards the center of the pocket and merge at their upper ends intolikewise inclined second partial surfaces (11), each of the secondpartial surfaces (11) ending in a third partial surface (12) which isparallel to the central vertical line (13).
 5. A cylindrical window-typecage of claim 4 wherein the crossbars (4) are profiled.